KR101228402B1 - Fast handover with reduced service interruption for high speed data channels in a wireless system - Google Patents

Abstract

A method of controlling a wireless communication system is provided. The method includes communicating data with a first base station, and selecting a switchover time for stopping communication with the first base station and initiating communication with a second base station. The switchover time is based on channel conditions associated with communications for the first and second base stations, such as SIR.

Communication system, data, target cell, serving cell, switchover, SIR.

Description

Fast handover with reduced service interruption for high speed data channels in a wireless system

1A is a block diagram of a communication system in accordance with an embodiment of the present invention.

1B illustrates an area in which the communication system of FIG. 1 may be used.

2 is a block diagram of one embodiment of a base station and a mobile device used in the communication system of FIG.

3 is a flow diagram illustrating the interoperation of various elements of the communication system of FIGS. 1 and 2.

Explanation of symbols on the main parts of the drawings

100: communication system 120: mobile device

125: data network 130: base station

138: RCN 160: public telephone system

165: CN 250: controller

The present invention relates generally to telecommunications and, more particularly, to wireless communications.

In the field of wireless communications, such as cellular telephones, a system generally includes a plurality of base stations distributed within the area serviced by the system. Various users in the area, fixed or moving, can access the system and, therefore, access other interconnected telecommunication systems through one or more base stations. In general, a mobile device maintains communications with the system by communicating from one base station to another as the user moves through the area as the user moves. The mobile device can communicate with the nearest base station, the base station with the strongest signal, the base station with sufficient capability to accommodate communications, and the like.

Conventionally, mobile devices are used for voice communications where the transfer of information is time-critical. That is, even if segments of a relatively short conversation are delayed or lost, it can substantially impair the meaning and understanding of the parties to the conversation. During the period when the mobile device stops communicating with the first base station and begins communicating with the second base station, there is a clear possibility that the communications will be at least temporarily interrupted or delayed. Thus, for voice communications, a process known as soft hand off (SHO) has been developed in CDMA and UMTS systems to have multiple connections in the overlapped coverage area so that conversations can be made with these transition periods. Substantially reinforces the possibility of continuing without easing.

Recently, the operation of mobile devices has been extended to high-speed data fields such as those that can be used when accessing the Internet or the World Wide Web. Unlike voice communications, high speed data exchange is historically not time-critical. That is, the transmission of data can be temporarily interrupted or delayed without affecting the recipient's ability to "understand" the data. Thus, transient delays or interruptions have been accommodated during the transition period from one base station to another.

However, the operation of high speed data connections has been extended to more time critical operations. For example, Voice over Internet Protocol (VoIP) is a process that includes digitizing voice signals, organizing digitized voice signals into packets, and sending packets over a high speed digital connection. to be. The receiving side reassembles the packets and reproduces the packets to generate audio communication. Thus, voice communications can be accomplished via a high speed data connection. If this process can be accomplished in real time, conversation can occur over a high speed digital connection. When a high speed digital connection is used for voice communications, transition periods become important to avoid delays or interruptions in conversation.

The present invention is directed to overcoming or at least reducing the effects of one or more of the problems presented above.

In one aspect of the present invention, a method of controlling a wireless communication system is provided. The method includes communicating information to a first base station and selecting a switchover time for initiating communication with a second base station. The switchover time is based on channel conditions associated with communications for the first and second base stations.

In another aspect of the present invention, a method of controlling a wireless communication system is provided. The method includes communicating information from a first base station and selecting a switchover time for initiating communication from a second base station. The switchover time is based on channel conditions associated with communications from the first and second base stations.

The invention may be understood by reference to the following description in connection with the accompanying drawings in which like reference numerals indicate like elements.

The invention is capable of various modifications and alternative forms of the specific embodiments, for example, in the drawings and the detailed description. The specific embodiment descriptions are not intended to limit the invention to the particular forms disclosed, and all changes, equivalents, and alternatives are intended to be included within the spirit and scope of the invention as defined by the appended claims. Understand your intent.

Exemplary implementations of the invention are described below. For clarity, not all features for an actual implementation are described in this description. In the development of any such practical embodiment, a number of implementation-specific decisions are made to achieve a developer's specific purpose, such as changing from one implementation to another in accordance with system-related and business-related constraints. Of course, you will understand. Moreover, it should be understood that such development efforts are complex and time-consuming, but nevertheless common practice to those skilled in the art that would benefit from the present disclosure.

In particular, with reference to FIG. 1A, a communication system 100 is shown in accordance with one embodiment of the present invention. For illustrative purposes, the communication system 100 of FIG. 1A is a Universal Mobile Telephone System (UMTS), and it is understood that the present invention is applicable to other systems that support data and / or voice communications. . The communication system 100 allows one or more mobile devices 120 to communicate with the Internet and / or a data network 125 such as a public telephone system (PSTN) 160 via one or more base stations 130. do. Mobile device 120 is connected to data network 125 and / or PSTN 160 via cellular telephones, personal digital assistants (PDAs), laptop computers, digital pagers, wireless cards, and base station 130. It can take the form of any of a variety of devices, including any other device capable of accessing.

In one embodiment, the plurality of base stations 130 may include T1 / EI lines or circuits, ATM virtual circuits, cables, optical subscriber lines (DSLs), and the like. It may be coupled to a Radio Network Controller (RNC) 138 by one or more connections 139. Although one RNC 138 is shown, those skilled in the art will appreciate that a plurality of RNCs 138 may be used to interface with a large number of base stations 130. In general, the RNC 138 operates to control and coordinate the connected base stations 130. RNC 138 of FIG. 1 provides replication, communications, runtime, and system management services, and transitions the transition of mobile device 120 during transitions between base stations 130, as discussed in more detail below. It includes adjusting.

As shown in FIG. 1B, the area 170 serviced by the system 100 is divided into a plurality of areas or cells, each associated with an individual base station 130. In general, each cell has a plurality of neighboring neighbor cells. For example, cell 175 has six neighboring cells 176 through 181 such that mobile device 120 entering into cell 175 may travel from one of neighboring cells 176 through 181. Can be. Thus, when mobile device 120 enters cell 175 from any of the neighbor cells 176-181, the mobile device enters neighbor cell 176-181 from the communication with cell 175. It is necessary to change by communication with).

Referring again to FIG. 1A, the RNC 138 also couples to a Core Network (CN) 165 via a connection 145 and connects T1 / EI lines or circuits, ATM virtual circuits, cables. , Optical digital subscriber lines (DSLs), and the like may take any of a variety of forms. In general, CN 165 acts as an interface to data network 125 and / or public telephone system (PSTN) 160. CN 165 performs various functions and operations, such as user authentication, but a detailed description of the structure and operation of CN 165 is not essential for an understanding of the present invention. Thus, to avoid unnecessary confusion in the present invention, additional descriptions of CN 165 are not here.

Thus, those skilled in the art understand that the communication system 100 enables the mobile devices 120 to communicate with the data network 125 and / or the PSTN 16. However, the configuration of the communication system 100 of FIG. 1A is illustrative in nature and it is understood that fewer or additional elements may be used in other embodiments of the communication system 100 without departing from the spirit and scope of the present invention. I understand.

Unless otherwise stated or apparent in the present discussion, terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or the like refer to the operation of a computer system or similar electronic computing system device and the like. Regarding processes, they resemble data presented as physical, electronic quantities in registers and memories of computer systems in physical quantities in memories or registers of computer systems or other such information storage, transfer or display devices. Manipulates and converts to other data presented.

Referring now to FIG. 2, shown is a block diagram of one embodiment of a functional structure associated with an example base station 130 and a mobile device 120. Base station 130 includes an interface unit 200, a controller 210, an antenna 215, and a plurality of channels, such as a shared channel 220, a data channel 230, and a control channel 240. In the described embodiment, the interface unit 200 controls the flow of information between the base station 130 and the RND 138 (see FIG. 1). The controller 210 generally controls the transmission and reception, controls the signals on the antenna 215 and the plurality of channels 220, 230, 240, and passes the minimum portions of the received information through the interface unit 200. Operate to communicate with the RNC 138.

Mobile device 120 shares certain functional attributes with base station 130. For example, mobile device 120 includes a controller 250, an antenna 225, and a plurality of channels, such as shared channel 260, data channel 270, and control channel 280. The controller 250 generally operates to control both transmission and reception of control signals and data over the antenna 225 and the plurality of channels 260, 270, 280.

Typically, channels 260, 270, 280 in mobile device 120 communicate with corresponding channels 220, 230, 240 in base station 130. Under the operation of the controllers 210, 250, channels 220, 260; 230, 270; 240, 280 are used to perform controlled scheduling of communications from the mobile device 120 to the base station 130.

Referring now to FIG. 3, a flow diagram illustrating the interoperation of various components of system 100 is shown. In the flowchart of FIG. 3, it is assumed that high speed data transmission is in progress for the mobile device 120, and the mobile device 120 communicates with the base station A, but transitions to the base station B. Initially, mobile device 120 is in a cell associated with base station A and accesses or enters a cell associated with base station B.

3 schematically illustrates a handover procedure for a high speed data channel and outlines a messaging process that may be used to switch a high speed data channel from a serving cell to a target cell. In general, the actual switchover is when the RNC 138 sends Radio Link Reconfiguration Commit messages to the serving node to stop the scheduled transmission at a prescribed " activation time. &Quot; When sending to B), start. The mobile device 120 begins to "listening" scheduling information from the target cell at activation time after sending "Physical Channel Reconfiguration Complete" messages. An important factor in reducing VoIP service interruption is the setting of an "activation time" for switching over from the serving cell to the target cell. Conventionally, an "activation time" is set at a very early stage of radio link reconfiguration commit messages, and is executed at the time that mobile device 120 sends "Physical Channel Reconfiguration Complete". In some prior art systems, setup time and execution time may be separated by significant amounts of time (eg, from hundreds of milliseconds to several seconds). The "activation time" is determined based on the process time of signaling messages (eg, Iur, Iub and UU). During this interval, various factors can negatively affect radio channel conditions. For example, mobile device 120 may move away from the serving cell, and the radio link quality may be significantly degraded so that data may no longer be delivered. In addition, the mobile device 120 may not be able to decode scheduling information and lost data. Thus, VoIP service for mobile device 120 may be interrupted for a significant amount of time. In one embodiment of the invention, the activation time for the switchover process may be carefully selected based on the current conditions of the wireless link between the mobile device 120 and the serving and target base stations.

In the first embodiment of the present invention, as shown in FIG. 3, the serving RNC 138-1 is connected to the mobile device 120 and the target from the high speed communication between the mobile device 120 and the source base station 130-1. It is determined whether to switch over to high speed communication between the base stations 130-2. The serving RNC 138-1 prepares a RNSAP (Radio Link Reconfiguration Ready) message, which is sent to the drift RNC 138-2 at step 300.

In the described embodiment, the source and target cells are controlled by different base stations 130-1 and 130-2. In step 302, the drift RNC 138-2 is configured to perform synchronous radio link reconfiguration using the NBAP (Node B Application Part) message “Radio Link Reconfiguration Prepare”. The source base station 130-1 is requested. In step 304, the source base station 130-1 returns an NBAP message "Radio Link Reconfiguration Ready".

In step 306, the drift RNC 138-2 requests the target base station 130-2 to perform synchronous radio link reconfiguration using the NBAP message “Radio Link Reconfiguration Ready”. In step 308, target base station 130-2 returns an NBAP message " Ready to reconfigure radio link. &Quot; In step 310, the drift RNC 138-2 returns the RNSAP message “Radio Link Reconfiguration Ready” to the serving RNC 138-2. In step 312, the drift RNC 138-2 initiates setup of new Iub Data Transport Bearers using the Access Link Control Application Protocol (ALCAP) protocol. This request includes AAL2 (ATM Adaptation Layer type 2) Binding Identity to bind the Iub data transport bearer to the high speed data channel.

At step 314, serving RNC 138-1 initiates setup of a new Iur data transfer bearer using the ALCAP protocol. This request includes the AAL2 binding identification to bind the Iur data transfer bearer to the high speed data channel. A high speed data channel transmission bearer for the target base station 130-2 is established. In step 316, the serving RNC 138-1 proceeds to the drift RNC 138-2 by sending an RNSAP message “Radio Link Reconfiguration Commit”. The activation time is selected in the form of a serving RNC 138-1 CFN (Connection Frame Number).

At step 318, the drift RNC 138-2 sends an NBAP message "Radio Link Reconfiguration Commit" to the source base station 130-1 including the activation time. Similarly, in step 320, the drift RNC 138-2 sends an NBAP message “Wireless Link Reconfiguration Commit” to the target base station 130-2 including the activation time. At the indicated activation time, the source base station 130-1 stops transmitting and the target base station 130-2 starts transmitting to the mobile device 120 on the high speed data channel.

Further, in step 322, the serving RNC 138-1 sends an RRC (Radio Resouce Control) message “Physical Channel Reconfiguration” to the mobile device 120. At the indicated activation time, mobile device 120 stops receiving high speed data at the source cell and starts receiving high speed data at the target cell. At step 324, device 120 returns an RRC message “Physical Channel Reconfiguration Complete” to serving RNC 138-1. At step 326, the drift RNC 138-2 initiates release of the old Iub data transfer bearer using the ALCAP protocol. Similarly, at step 328, serving RNC 138-1 initiates the release of the old Iur data transfer bearer using the ALCAP protocol.

In order to reduce or minimize VoIP service interruption during handover, the "activation time" needs to be appropriately selected. The "activation time" is determined by the processing time of the signaling procedure. If the switchover is set very late and the radio channel conditions of the serving cell are degraded, the VoIP service has an open window period of no service. If the activation time is set very quickly and the radio channel conditions of the target cell associated with a particular user are not good, the VoIP service will also have an interruption. The problem with switchover timing is that the radio channel condition is unknown when the RNC 138-1 sets the activation time. In order to identify the best switchover timing, L-3 signaling for communication between the mobile device 120 and the RNC is required. Nevertheless, L-3 signaling delay greatly affects the effect of switchover timing identification. Thus, the criteria for minimizing VoIP service interruption during handover are to accurately estimate the required signaling processing time, to reduce the signaling time, and to switch over to the target cell at the correct time.

During the switchover, reducing the time needed for signaling can improve the switchover process. To trigger the switchover and estimate the desired switchover time, the RNC 138 sends an SIR (Signal to Interference Ratio) from the base stations 130 in the mobile or active set reported in the best cell measurement. Use feedback of radio channel conditions such as However, the accuracy of the estimation decreases as the prediction interval becomes larger. In particular, the wireless channel conditions can vary greatly in the hundreds of milliseconds to several seconds. By reducing the interval, the switchover process can be substantially improved.

Base station 130 periodically reports SIR measurements to RNC 138. In one embodiment, the average SIR is calculated over an 80 ms interval and reported to the RNC 138. The average SIR measurement may be used as a reference for the wireless channel conditions of each leg during switchover. Average uplink SIR measurements correspond to the long term average of CQI reports for the downlink radio link. In an embodiment of the invention, the algorithm used to calculate the "activation time" is as follows.

Here, the SIR _serving and the SIR _target are SIR measurements of the serving cell and the target cell, respectively, and the Threshold _serving and the Threshold _target are thresholds of the serving cell and the target cell, respectively. The algorithm is designed based on link imbalance during switchover when uplink inner loop power control speeds up the transfer of the radio link for a leg with good channel conditions. Thus, the activation time setting can be improved by setting the threshold appropriately according to the signaling process delay.

General signaling procedures for switching the high speed data channel from the serving cell to the target cell are performed continuously. Since the Iub radio link reconfiguration commit message does not require acknowledgment, at approximately the same time or at least in part, overlap, send Iub radio link reconfiguration messages to the serving and target cells, and send a UU RRC physical layer reconfiguration message to the mobile. The delay can be reduced by sending to device 120. This eliminates significant delays and introduces only minimal process delays.

The processing delay of the UU RRC physical channel reconfiguration message is another delay factor, along with the current Iub and UU signaling message to commit the switchover of radio links at activation time. The current execution procedure for physical channel reconfiguration (see section 13.5.2 of TS25.331) is 80 ms after the mobile device 120 receives the UU signaling message and updates the L1 configuration at the beginning of the next TTI. Ask to run this within The DCCH RABs supported in TS34.108 are 1.7 kbps, 3.4 kbps, and 13.6 kbps, with TTIs of 80, 40, and 10 ms, respectively. The most common general test procedure is 3.4 kbps DCCH with a 40 ms TTI. When the 3.4 kbps DCCH is used to carry physical channel reconfiguration messages for high speed data channel handover, the total delay exceeds 120 ms (80 ms processing + 40 ms TTI DCCH reception). Moreover, the 80 ms execution delay is also taken into account by the low signaling RAB for the primitive communication between the higher layer protocols and the physical layers in the mobile device 120. Using a 13.6 kbps RAB with a 10 ms TTI reduces execution time and processing time. This will reduce the interruption of the VoIP service during switchover.

One important problem with high speed data channel switchover is to synchronize the buffers at the base stations 130-1 and 130-2, where the Iub links for the serving cell and the target cell are established prior to the radio link reconfiguration commit commands. Because it becomes. To reduce service interruption, the RNC 138 may send VoIP data to both base stations 130-1 and 130-2 after the Iub data link of the target base station 130-2 is established. have.

The target base station 130-2 does not schedule any transmissions before the "activation time" and will not have the idea of information being scheduled to the source base station 130-1. Because other channels (eg, UL DPCH) are operating in soft-handover mode, the target base station 130-2 may not be able to send to the source base station 130-1 before the "activation time". Ack / Nack and CQI information can be decoded. Because of link imbalance during switchover, the target cell initially incorrectly decodes Ack / Nack and CQI for the serving cell with erasure and moves to progressively correct decoding before the "activation time". Once Ack / Nack and CQI are erased, the target cell may decide to _{drop the} VoIP frame every T _erase interval. The T _erase interval is a parameter that is optimized to minimize buffer occupancy in the target cell. If the Ack is correctly decoded in the target cell before the activation time, the target cell may decide to drop the next VoIP packet. This procedure is unregulated VoIP counting for the high speed data channel when the VoIP packet is sent to both the serving and target cells during the switchover prior to the activation time. This will prevent any data gaps on the sequence transport of VoIP packets and will minimize buffer occupancy in the target cell. The proposed algorithm is called "Pseudo-Synchronization" because the action is similar to buffer synchronization.

Those skilled in the art will appreciate that the various system layers, routines, or modules described in the various embodiments herein may be executable control units (such as controllers 210 and 250 (see FIG. 2)). I understand. Controllers 210 and 250 may include a microprocessor, microcontroller, digital signal processor, processor card (including one or more microprocessors or controllers), or other control or computing devices. Storage devices referred to in this description may include one or more machine-readable storage media for storing data and instructions. Storage media includes dynamic or static random access memories (DRAMs or SRAMs), erased and programmable read-only memories (EPROMs), electrically erased and programmable read-only memories (EEPROMs), and flash memories. Same semiconductor memory devices; Magnetic disks such as fixed, floppy, removable disks; Other magnetic media including tape; And different forms of memory, including optical media such as compact discs (CDs) or digital video discs (DVDs). Instructions to make up various software layers, routines, or modules in various systems may be stored in respective storage devices. The instructions executed by the controllers 210, 250 cause the corresponding system to perform the programmed actions.

It is apparent to those skilled in the art having the benefit of the teachings herein that the specific embodiments described above are for illustration only, and that the invention can be modified and implemented in different but equivalent ways. Moreover, it is not intended to be limited to the details of construction or design shown herein. As a result, the method, system, and portions of the described method and system may be implemented at different locations, such as a wireless unit, base station, base station controller, and / or mobile switching center. Moreover, the processing circuitry required to implement and use the described system includes, but is not limited to, application specific integrated circuits, software-driven processing circuitry, firmware, programmable logic devices, as understood by one of ordinary skill in the art having the benefit of this disclosure. It may be implemented in hardware, discrete elements or arrangements of such elements. Certain embodiments disclosed above may be altered or modified and such changes are considered within the scope and spirit of the invention. Therefore, the protection scope pursued here is presented by the following claims.

Mobile devices are used for voice communications in the delivery of time critical information. That is, even if segments of a relatively short conversation are delayed or lost, it can substantially impair the meaning and understanding of the parties to the conversation. During the period in which the mobile device communicates discontinuously with the first base station and begins communicating with the second base station, there is a clear possibility that the communications are at least temporarily interrupted or delayed.

Voice communications can be accomplished via a high speed data connection. If this process can be accomplished in real time, conversation can occur over a high speed digital connection. When a high speed digital connection is used for voice communications, transition periods become important to prevent the conversation from being delayed or interrupted.

The present invention is directed to overcoming or at least reducing the effects of one or more of the problems presented above.

Claims (10)

In a method for controlling a communication system: Communicating data to a first base station; And Selecting a switchover time for initiating communication with a second base station, the switchover time comprising the selection step based on channel conditions associated with communications for the first and second base stations, The switchover time is selected in response to at least one of an SIR associated with communications for the first base station falling below a preselected threshold and an SIR associated with communications for the second base station rising above a preselected threshold. , Communication system control method. The method of claim 1, wherein selecting the switchover time for initiating communication with the second base station is based on an SIR associated with the communications for the first and second base stations. Selecting the switchover time for initiating communication with the second base station. delete delete 3. The method of claim 2, wherein selecting the switchover time for initiating communication with the second base station, wherein the switchover time is based on an SIR associated with communications for the first and second base stations. The switchover for initiating communication with the second base station when the SIR associated with communication for the first base station falls below a preselected threshold and the SIR associated with communication for the second base station rises above a preselected threshold Selecting a time further. 2. The method of claim 1, further comprising sending a reconfiguration message to the first and second base stations to allow communication with the second base station to begin. 7. The method of claim 6, wherein sending the reconfiguration message to the first and second base stations to allow communication to begin with the second base station comprises: allowing to initiate communication with the second base station. Simultaneously transmitting the reconfiguration message to the first and second base stations. 7. The method of claim 6, wherein sending a reconfiguration message to the first and second base stations to allow communication to begin with the second base station overlaps to allow communication to begin with the second base station. Transmitting the reconfiguration message to the first and second base stations during overlapping time intervals. 2. The method of claim 1, wherein communicating data to the first base station further comprises communicating data to the first base station via a high speed data channel. 2. The communications system of claim 1, further comprising communicating data to both the first and second base stations after the switchover time is selected and during a first time period before actual switchover occurs. Control method.

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